On 22 maj 2010, at 07.40, Don wrote: >> The SATA power connector supplies 3.3, 5 and 12v. A "complete" >> solution will have all three. Most drives use just the 5v, so you can >> probably ignore 3.3v and 12v. > I'm not interested in building something that's going to work for every > possible drive config- just my config :) Both the Intel X25-e and the OCZ > only uses the 5V rail. > >> You'll need to use a step up DC-DC converter and be able to supply ~ >> 100mA at 5v. >> It's actually easier/cheaper to use a LiPoly battery & charger and get a >> few minutes of power than to use an ultracap for a few seconds of >> power. Most ultracaps are ~ 2.5v and LiPoly is 3.7v, so you'll need a >> step up converter in either case. > Ultracapacitors are available in voltage ratings beyond 12volts so there is > no reason to use a boost converter with them. That eliminates high frequency > switching transients right next to our SSD which is always helpful. > > In this case- we have lots of room. We have a 3.5" x 1" drive bay, but a 2.5" > x 1/4" hard drive. There is ample room for several of the 6.3V ELNA 1F > capacitors (and our SATA power rail is a 5V regulated rail so they should > suffice)- either in series or parallel (Depending on voltage or runtime > requirements). > http://www.elna.co.jp/en/capacitor/double_layer/catalog/pdf/dk_e.pdf > > You could 2 caps in series for better voltage tolerance or in parallel for > longer runtimes. Either way you probably don't need a charge controller, a > boost or buck converter, or in fact any IC's at all. It's just a small board > with some caps on it.
I know they have a certain internal resistance, but I am not familiar with the characteristics; is it high enough so you don't need to limit the inrush current, and is it low enough so that you don't need a voltage booster for output? >> Cost for a 5v only system should be $30 - $35 in one-off >> prototype-ready components with a 1100mAH battery (using prices from >> Sparkfun.com), > You could literally split a sata cable and add in some capacitors for just > the cost of the caps themselves. The issue there is whether the caps would > present too large a current drain on initial charge up- If they do then you > need to add in charge controllers and you've got the same problems as with a > LiPo battery- although without the shorter service life. > > At the end of the day the real problem is whether we believe the drives > themselves will actually use the quiet period on the now dead bus to write > out their caches. This is something we should ask the manufacturers, and test > for ourselves. Indeed! /ragge _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
